Short exposure X-ray system



July 7, 1936. w A MCKAY SHORT EXPOSURE X-RAY SYSTEM Filed June 1, 1935 HIIIIIIIII INVENTOR h/. A. M. lf/l Y. w 7

ATTORNEY isired times.

Patented July 7, 1936 STATES SHORT EXPOSURE X-RAY SYSTEM William A. McKay, Essex Fells, N; J assignor to Westinghouse Lamp Company, a corporation of Pennsylvania provement thereon.

v In the system shown in the above noted application a high tension source of' electrical energy is arranged to supply unidirectional current to an energy storage device, which upon being completely charged is caused to discharge through the X-ray tube thus energizing the same with attendant generation of X-rays. A switching device comprising a thermionic discharge device is connected in a series circuit with the X-ray tube and energy storage device which is operable to prohibit discharge of the energy storagedevice until the latter is charged to its full capacity. Upon the accumulation of the desired charge of energy in the energy storage device the series connecteddischarge device is operable in response to actuation by an operator to cause substantially instantaneous discharge of the energy storage device with resultant energization of the X-ray tube untilthe complete charge of the energy storage device is dissipated. a

It has been found, however, that while the series connected discharge device is positively operable for the purposes intended at'X-ray operating potentials of approximately'75 to 100 kilovolts no discharge device is, up to the present time, known to the art which will satisfactorily prohibit discharge or an energy storage device of large capacity or the flow of current from a high potentialsource having a potential in excess of 100 kilovolts.

This is due to the fact that the materials of which the electrodes of the controlling discharge devices are constructed are inherently limited to la rather definite maximum potential. When the electrodes of the device are subjected to this max- -imum potential, or the same exceeded, this high potential causes the emission of electrons from the metallic electrodes commonly referred to as cold discharge.

It naturally follows that when this device is connected in series with the X-ray tube and the high potential source and a discharge occurs in the controlling discharge device energy is immediately supplied by the source to the X-ray tube with attendant generation of X-rays at unde- Moreover, even when the high potential to whichthe controlling discharge device is subjected is maintained slightly below the maximum potential the same can withstand without cold discharge occurring, this potential frequently has a destructive effect upon the device upon operation thereof due to the substantially instantaneous rush of current therethrough if the potential is too near the maximum the device can withstand without breakdown.

By my present invention I obviate these present difficulties by interposing a three electrode thermionic discharge device between the high potential source and the anode of the X-ray tube and a similar discharge device between the high potential source and the cathode of the X-ray tube. This arrangement subjects one of these discharge devices to a potential having a positive polarity equal to only one half of the total potential of the source and the other discharge device to a negative potential likewise equal to one half the totalpotential of the source. 7

The control electrode or grid of each respective discharge device is impressed with a potential from separate auxiliary sources to prevent energization of the X-ray tube and these auxiliary sources are simultaneously rendered operative to cause each respective discharge device to become inoperative to prevent and operative to cause energization of the X-ray tube by the high tension source. 7

Accordingly each respective discharge device,

being subjected to only one half the potential of the source and capable of biocking currents of approximately 1000 milliamperes at 100kilo- .volts, enables the construction of a short exposure X-ray system in which the X-ray tube may I be energized by a potential substantially double that of such system heretofore known to the art.

Moreover, while I have shown my presentinvention as adapted to an X-ray system for the taking of short exposure X-ray photographs wherein 40 the X-ray tube receives energization from an energy storage-device as shown in the aforementioned copending application, it is to be understood that the same is readily applicable to X-ray systems of various other types. "For example, .45 by the employment of my present invention energization of the X-ray tube may be so controlled that instead of causing the entire energy of an energy storage device to discharge substantially instantaneously through an X-ray. tube I may make this discharge gradual .over any desired period of time regardless of the magnitude of the potential accumulated in the energy storage device. By the utilization of a discharge device in series with each of the electrodes of the X-ray pulsating potential X-ray systems for the taking of radiographic exposures but the same is equally adaptable to deep therapy'systems of exceedingly high potential. V

Inasmuch as each of the controlling discharge devices when connected in series with each of the "electrodes of the 'X-ray tube is subjected to onlypotential of the latter may be-increased to an "extent even greater than that at which breakdown of the individual discharge devices will occur. Thus by interposing additional discharge devices in series with each other and each of the-electrodes of the tube in tandem arrangement the potential to which each device is sub jected is further reduced with the addition of each pair of devices. When it is desired toc'ause energization of the X-ray'tube it is merely necessary t'o cause the simultaneous operation of all of' the controlling discharge devices. 7 It is accordingly an object of 'my'invention to provide a system for taking short exposure X-ra'y photographsin which the energy supplied by a high'potential source to'the'X-ray tube may v "be controlled accurately With respect to the time and quantityi g g 1 Another object of my invention is the provision of a switching means inthe highten'sion circuit 7 of 'an x ray tubesystem which is subjected to only one-half the total potential suppliedto 'the Xaaytube and operative to normally prevent the How of energyfromflthe source to the tube, but readily-operable to cause instantaneous energiaation of the tube. V g

Another object of my invention is the provision of an X-ray system for taking short exposure photographs employing a -plu rality oi thermionic discharge devices in series with the X-ray ftube and source of energization'therefor, which are provided with control electrodes having a potential impressed thereupon normally preventing fthQflOW through the respective discharge {devicefsand consequently the X-i'ay tube and which are adapted to. assist the fiowof energy when impressed with an opposite po1arity.-

- A further object of my invention is the .pro-

'ffvisionf'of a. system for taking short; exposure 'X rayphotographs in which the ene'rgyfor' sup- ;tion"of a system for taking short ex osurexaay;

70 .is shown in the central part of .in'giflgure enclosed by the dotiand dash'line-therekin shown; This generatingsystem may bev of d inwhich the'suppl'y of energy therefrom is controlled with; minute precision with an absence of appreciable time lag.

Still further objects of my invention' will be fcome apparent to those skilled in the art-by reference to the accompanying drawing in' which "the 'single figure is a. diagrammatic repre'senta photographs showing one form which myinven- .tion may take.

"shown-a suitablesource of cornmercial alternah ing'potentiaLsuch as conductors ana L2. com nected tothese conductors is 'a hightension heavy current generating system which is arranged to supply energy to the'X-ray' tube.

;any suitable type, such as a high tension transformer 5,7 the primary 6 of which is-connected I 'plyin'gthe 'X-raytube is taken from a condenser 1 Referring now to the drawing in d taiirhave This generator the accompanydirectly to the commercial source of potential Ll V and L2. M V V g The secondary winding I. of this high tension transformer is connected to the cathode of a rectifying valve tube. 8 by means of a conductor.

,means of a conductor. l5-to a condenser l6. 'These one ,half the potential .of the source the total.

limits the insulation requirements of the high 1' potentialsystemto one-half the total output enj f ergy of this secondary winding 1. During alter 7:0

munghalrwaves of the; alternating current'oycle the energy generated in J the secondary winding 1 is adapted to store relatively heavy currems or between" 5f 00. and' l,000' :milliampe'res at lUO in the condensers. and I 6, which are of acapaci'ty 'slifil'cient to the chargedrwiththis ener Although-I haveshown what is terme in the art as half wave rectificatiomtha't ls to fsa'y, the

condensers are charged only during one-halt wave ofthe-alterna'ting current cycle it should so u be readily understood that any other hig-h voltage I generating'system is as readily adaptabi'e'for the I generation of the requisite currents anti thatithe; same may be full wave rectificationl-nFlieuaifl which I have shown mere-35 i half waveir'ectification, 7 1y for the purposes of simplicity.

AnX-ray'tube 20111 5 its oath ode and connect ed to the anode of a thermionic discharge device 5 21 by :means' ofa conductor- 23 and the anode of theeX-ray tubeds connected by means ot a. I

conductor '24 'to thecathode of 'asimilar onic discharge device 2. 'Ih'ecathode 'oIIthe dis- 7 charge "device 221's 'connectedby means of a con :ductorltf to the negative plate "of condenser. 11 y and ma .:-similar manner the positive plate :of

condenser 16' is connected "by 'means of a corr- .ductoir 21w .theia'node of a thermionic discharge device 25. This accordingly i'orm's circuit for th'efcondensers I4 and i6 whichfim eludes: the ixqaymbszn and the discharge de+ 1 g y 50 vices :5 .eormected in series therewith This circuit which suppiies highpotentialenergy i to the Xf ray*tub'e, including the m cnargeua- 3 *vl'ces' 22 2}, naturally. subjects latter devicesito' the samehi'ghpotential current mug iof th'e x' ray tube :andilt is essential they flthe :saine'current-voltage characteristics as. V X-raytube in order to; withstand tneasamezen- I "ergy. The thermionic cathode of the E20 is arrangedftovreceive low tension heati n'urrents from a h'eating transformer :28; th'e pcri f V .j maryso'fwhich IsconnEoted totheconn erciall sourc'efof supplynl 'and V :In a *similarmanner the cathode-o! "oni'c device?! i's a'daptedto'receive heatingicur- :ing traasrormer ta'tneprimar or which is slim; l l'arly:connectedtothecoimnercial'source ofsupply LI and L2. The cathode of rectifying valve 8 reeeivesiheating suitably l .r'ent'througha-pairmfoonductors '2 9 30 from T a low tension transformer 32,"' the primary or} which is connected to the connnerci'al sourceof 1 cu rm nt -rrom a lowtensi cam-ta former 36 and in a similar manner the cathode of rectifying valve ll! receives heating current from a low tension transformer 31, with the primaries of both of these latter transformers being also connected to the commercial source of supply LI and L2.

The discharge devices 22 and 25 in addition to their anodes and cathodesare each provided with a control electrode in the form of a grid. The control electrode of each of these thermionic discharge devices is adapted to have a suitable potential from separate auxiliary sources impressed thereupon which is normally of sufiicient magnitude to prevent a positive potential from. being impressed upon the anode of the X-ray tube by the source, or condenser is, and a negative potential from being impressed upon the cathode of the X-ray tube by the source or condenser M despite the high potential energy to which they are subjected. Consequently electrons are prohibited from flowing between the cathode and anode of each respective discharge device and the oathode and anode of the X-ray tube thus effectively preventing energization of the latter.

Accordingly the auxiliary source for the control electrode of the discharge device 22 comprises a transformer 4 l, having its primary winding connected to the source of supply Ll, L2 and its secondary winding 42 connected at one end to the anode of a rectifying valve 43 by means of a conductor 44, and its remaining end is connected by means of a conductor 45 to the anode of another rectifying valve 46. The thermionic cathodes of the respective valves 43, 45 are connected together and to one plate of a condenser 41, through a resistance 48, by means of a conductor 49. The midpoint of the secondary winding 42 is in turn connected, by means of a conductor 55, to the negative plate of the condenser 41 and to one end of the secondary winding 52 of a transformer 53, the primary of which is connected to the source of supply Ll, L2, and in addition the conductor is connected to the positive plate of a second condenser 54.

The remaining end of the secondary winding 52 is connected by means of a conductor 55 to the cathode of a rectifying valve 55 and the anode of this latter valve is connected by means of a conductor 51 through a high resistance 58 to the negative plate of the condenser 54. The cathodes of the rectifying valves 43 and 45 receive heating current from a low tension source of supply through a pair of conductors 59 and 60 which extend to a low tension secondarywinding 52, and in a similar manner the cathode of rectifying valve 56 receives heating current from a low tension secondary winding 53, with both of these secondary windings B2 and 53 comprising a tertiary winding wound upon the core of the transformers 4| and 53, or, if preferred, may extend to separate heating transformers.

' This auxiliary source of potential is arranged to store energy during each half wave of the alternating current cycle in the respective condensers 41 and 54 which are arranged to discharge at desired periods of time through an output circuit. A conductor 64 extends from the negative plate of condenser 54 to the control electrode of the discharge device 22 and a similar conductor 65 extends from the cathode of the thermionic discharge device 22 to the positive plate of condenser 54 and negative plate of condenser 41.

Accordingly upon energization of the transformer 53 the secondary winding 52 will supply energy to the condenser 54 during a half wave of the alternating current cycle. For example, when one end of the winding 52 to which the conductor 55 is connected has a negative polarity electrons will flow therefrom through conductor 55, rectifying valve 55, conductor 51 and high resistance 58, through the negative plate of the condenser 54 and thence from the positive plate of condenser 54 through conductor 5G back to the remaining end of secondary winding 52. The condenser 54 is of such capacity as to be stored with energy having a potential of approximately 5,000 volts and as the negative plate thereof is connected by means of conductor 54 to the control electrode of the discharge device 22,- a negative potential at this voltage will be impressed upon the control electrode of the latter discharge device. This is of sufficient magnitude to prevent the flow of electrons from the cathode to the anode of the discharge device 22 and consequently prevents any energy from the condenser i4 flowing to the cathode of the X-ray tube 20.

At the same time that energy is being stored by the transformer 53 in the condenser 54 the secondary winding 42 will store energy in the condenser 41. Accordingly regardless of the particular polarity of either end of the secondary winding 42 electrons will flow through conductor 55 to the negative plate of condenser 41 and thence from the positive plate through conductor 49, resistance element 48, and thence by means of either the valve 43 or 46, and conductors 44 and 45 respectively, back to one end of the secondary Winding 42 depending upon the instantaneous polarity of either end of this winding. For example, if the end of the wind ing 42 to which the conductor 44 is connected is at a given instant positive with respect to the midpoint of the winding electrons will flow through the valve 43 and conductor 44 back to the winding 42, while at this given instant the be negative and consequently electrons will not flow through the rectifying valve 45. However, when this end becomes positive and the end to which the valve 43 is connected becomes negative then electrons pass through rectifying valve 46 and conductor 45 back to the opposite end of winding 42.

Upon initial energization of the transformer 4! from the source of supply Ll, L2 the resistance element 48 functions to limit the initial surge of energy supplied to the condenser 41 to protect the insulation of this transformer.

It is well recognized that the phenomena of operation of condensers upon being initially charged is similar to a direct short circuit impressed upon the source due to the sudden rush of current to the condenser until the same become charged. This would ordinarily impress a very heavy load upon the valve tubes 43 and 46, but due to the reaction of the resistance element 48 this is prohibited, as well as aninitial heavy surge upon the transformer 4!. Also the resistance element 58 functions to limit the initial surge of energy supplied to the condenser 54 to protect the valve tube 55 and transformer, 53, and in addition causes an IR drop in this circuit to the current flow in order to impress a nonfluctuating negative potential upon the grid of discharge device 22. When it is desired to impress a positive polarity 0 opposite end of the winding 42 must necessarily til total potential of the source and also one-half the potential of the source to ground. Moreover, as the potential impressed upon discharge device 25 is positive with respect to ground and that of discharge device 22 negative with respect thereto separate auxiliary sources are necessarily required for impressing a potential upon the grids of the respective discharge devices.

In the operation of my system for taking short exposure X-ray photographs the cathodes of all the valve tubes and X-ray tube are first brought to incandescence and the transformers 4|, 53 and I4, 16 connected to the commercial source of supply by means of a suitable switch or switches, not shown. This initially impresses a negative potential upon the control electrodes of the respective discharge devices 22 and 25 as the hand switch 88 is at this time in its normal or opened position. A suitable switch, not shown, is then closed which connects the primary winding 6 of the transformer 5 to the commercial source of supply LI and L2, thus causing the high voltage heavy current condensers l4 and Hi to become fully charged, after which the switch is opened to prevent any repetition of charging of the condensers immediately following their discharge.

The hand switch 88 is then closed to cause operation of the relay 66 with attendant reversal of the polarity impressed upon the control electrodes of the respective discharge devices 22 and 25 in the manner previously explained. This immediately enables substantially an instantaneous discharge of the condensers l4 and I6 through the X-ray tube upon the consummation of reversal of the polarity impressed upon the control electrodes of the discharge devices 22 and 25 with attendant generation of X-rays by the X-ray tube.

It thus becomes obvious to those skilled in the art that I have provided an X-ray system for taking short exposure X-ray photographs in which current flow in a high potential circuit and energization of the X-ray tube is positively prevented by means of thermionic discharge devices, which are provided with control electrodes.

By impressing a negative potential upon the control electrodes of these devices'having suflicient magnitude the high tension heavy current is completely blocked and energization of the X-ray tube prevented. Upon reversal of this potential impressed upon the control electrodes from negative to positive substantially instantaneous energization of the X-ray tube simultaneously occurs without variation in the energy supplied thereto and consequently a uniform intensity of the X-rays emanating from the X-ray tube results. Moreover as the respective discharge device is connected in series with one side of the high tension source and one of the respective electrodes of the X-ray tube each discharge device is subjected to only one half the total potential of the high voltage source.

Although I have shown and described one specific embodiment of my invention I do not desire to be limited thereto as other modifications of.

the same may be made without departing from the spirit and scope of the invention as set forth in the appended claims. 7

What isclaimed-z 1. An X-ray system for taking short exposure X-ray photographs comprising means for storing an electrical charge, an X-ray tube provided with an anode and a cathode and connected to said means, and means connected to said first mentioned means and said X'-ray tube and normally operative to entirely prevent said X-ray tube from being supplied with energy from said first mentioned means, said last mentioned means including an evacuated discharge device interposed between said first mentioned means and the anode of said X-ray tube and an evacuated discharge device interposed between said first mentioned means and the cathode of said X-ray tube,'said last mentioned means being operable to cause said first mentioned means to instantaneously supply energy to said X-ray tube.

2. An X-ray system for taking short exposure X-ray photographs comprising means for storing an electrical charge of high potential and current, an X-ray' tube having an anode and a cathode and connected to said means, an evacuated discharge device connected to said means and to the anode of said X-ray tube, a second evacuated discharge device connected to' said means and to the cathode of said X-ray tube, means connected to each of said discharge de-' vices for positively preventing current fiow there through and consequently from said first mentioned means to the anode and cathode of said X- ray tube, and means associated with said last mentioned means and operable to cause the same to become instantaneously inefiective to prevent and operative to cause current fiow through each of said discharge devices from said first mentionedmeans to the anode and cathode of said X- ray tube.

3. An X-ray system for taking short exposure X-ray photographs comprising an X-ray tube having an anode and a cathode subjected to high potential electrical energy upon energization of said tube, a pair of electron discharge devices each having an anode, a cathode, and a control electrode, a primary and a secondary circuit, said X- ray tube and discharge devices being connected in series in said secondary circuit, said devices having current voltage characteristics corresponding to said X-ray tube and subjected to the same potential as impressed respectively upon theanode and cathode of said X-ray tube upon energization of the same, means for impressing a predetermined negative potential and a predetermined positive potential upon the control electrode of one of said discharge devices, means for impressing a predetermined negative potential and a predetermined positive potential upon the control electrode of the other of said dischargedevices, and means included in both of said last mentioned means and operable at will for simultaneously altering the potential impressed upon the control electrode of both of said discharge devices.

4. An X-ray system for taking short exposure X-ray photographs comprising a source of direct' current of high potential, an X-ray tube having an anode and a cathode and connected to said source, an electron discharge device having an anode, a cathode, and a grid, and interposed between said source and the anode of said X-ray tube, an electron discharge device having an anode, a cathode, and a grid, and interposed between said source and the cathode of said X-ray tube, means for impressing a non-fluctuating negative charge upon the grid of said first mentioned discharge device to prevent the potential of said source from being impressed upon the anode of said X-ray tube, means for impressing a non-fluctuating negative charge upon the grid of said second mentioned discharge device to prevent the potential of said source from being impressed upon the cathode of said'X-ray tube, and means associated with both of said last mentioned means and operable to cause the same to change the sign of the charge impressed upon the gridof each respective discharge device and cause said" I sourceto energize said X-ray tube; r

o '5. In an 'X-ray systemffor taking short ex posure X-ray photographs the combination of an X-ray tube having an anode and a cathode, a pair o1" thermionic discharge devices each provided Z with an anode, a cathode, and a control electrode, a condenser of high potential and'large current capacity connected in a series circuit withsaid Y discharge." devices and said X-ray tube, for energiz'ing the-latter, means for storing energy in said condenser, means normally operative to impress a negative potential'upon the control electrode of one of said discharge devices to prevent said condenserirom impressing a potential upon-the anode of said X-ray tube, means normally 'op- 'erativeto'impress a negative potential upon the control electrode of the other of said discharge devices: to prevent'said condenser from impressing aipotential upon the cathode of said X-ray tube, andmeans associated with both of said last men'- tioned means and operable'to' cause both ofsaid means to-instantaneously remove the negative 7 potential from the control electrode of eaclrrespective discharge 'deviceand impress a positive potential thereupon to cause the simultaneous discharge of said condenser through each of said discharge devices with attendantv energization of said ,X-ray tube; V '6.;In an X-ray system for taking short expo sure X-rayiphotographs the combination of an X- ray tube having an anode and a cathode,asource of potential for energizing said: X-ray tube, a

thermionic discharge device connected with the anode of said X-ray tubeand said source, a secondithermionic discharge-device connected with the cathode of said X-ray tube andsaid source, each of said discharge devices being provided with arr-anode, a cathode, and an element normally operative to offe'r'an artificial resistance to the flow of current therethrough and consequently from said source to the anode and cathode of said X- ray' tube, and means'ior rendering the element of each respective device inoperative 'to 1 prevent the flow, of current 'and'operative to assist the flow of'current, through eachdevice and from said source to said X-ray tube. 7.- An X-ray system for taking short exposure X-ray photographs comprising an"X-ray tube having an anode and a cathode subjected to high potential electrical energy upon energization of .saidtube, a source of unidirectional high potential energy for supplying a high positive potential to the anodeand a high negative potential to the cathode of, said X-raytube,V-means-interposed betweensaid source and theanode of said X-ray tube having current voltage, characteristics corresponding to that of said 'Xray tube and subjected to the same positive potential supplied by said source and operative to prevent said source from impressing a positive potential upon theanode of said X-ray tube, means interposed between said source and the cathode of said X- 'ray, tube having current voltage characteristics corresponding to that of" said X-ray tube and subjected to the same negative potential supplied by said source and operative to prevent said source from impressinga negative potential'upon the cathode of said X-ray tube, and means asso: ciated with both of saidlast mentioned means and operative to cause said-source to supply a high positive and negative potential to said 'X-ray 'tubefor' the purpose of energizing the'latter.

" 8-.'In anX-raysystemior taking s hort'fex posure X-ra'y' photographs the combination of an ative to prevent ando'per'at-iveto cause saidsource X- raytube having, an anode and a cathode 'subjected to high potential energy ,upon energization of said tube, a source of grounded unidirectween said source and thecathode of 'saidX-ray tube subjected to la potential corresponding to that of said source with respect'to ground and V operative. to prevent: said source from supplying amegative potential to the cathode of said X-ray tube, and 'means electrically associated with both of said last mentioned means and operablci'to cause the same to simultaneously become inopertosupply a" high positive and negativepotential to'saidX-ray tubeior the purpose of "energizing the-latter. 7 v i:

9'; In an X-r-raysystem' for taking short' exposure X-raYphotographsthe combination. of-an X-raytube-ihaving an anode andia' cathode sub jectedtoiiigh potential energy upon en'ergization 'ofsaid"tube; a source of unidirectional highipo tential electrical" energy for :supplying a high positive potential to the-anode and a highne'gative '3 potential tothecathode "of said X-ray-tubefa i thermionic 'discharge' device provided: with'an anode, a cathode, and 'a grid, and interposed be-,

tween said "source and" the anode of said X-raytube, said: device having currentvoltagecharacteristics" corresponding 'to that ot.,saidrx-ray tube "and subjected tofthe same positive potential suppliediby said source to said 'X-ray tube, an auxiliary source of relatively low potential connected to the" grid of saiddischargedevice and normally operative to impress a negative potential upon said gridtopreventa high positive apotene e, 1 tial being supplied by said high potential source to the anode of said X-ray tube, an auxiliary source or potential adaptedto beconnected to thegridof said discharge device for supplying a positive potential thereto," a thermionic. discharge deviceprovided with an anode, a cathode,

anda grid and'interposed between said source and the cathode of saidX-ray tube, said second mentioned device having current voltage characteristics corresponding 'to'that of said X-raytube and subjected to the same negative potential sup- 1 plied bysaid' source to said X-ray tube, an auxtothe grid "of said last mentioned dischargede vicefand normally operative to impress; a negative potential upon said grid to prevent a high negative potential beingrsupplied' by said high 'iliary'source'of relatively low potential connected potential: source 'to the-cathode ofsaid X-ray tube, an auxiliary 'sourceof potential'adapted to "be connectedtof the grid of said second mentioned discharge device for supplying a positive potential thereto, and a relay electrically assocause both of said, auxiliarytsources supplying ciated with all of, said auxiliaiy's'ources and operable in response to-actuation by an operatorto a negative potential to the gridsof the respective discharge devices to become ineffective and to connect the remaining auxiliarysources to the grids of the respective discharge devices for the purpose of impressing a positive potential thereupon, to enable said high potential source to supply a positive and negative potential to said X-ray tube and energize the same.

10. An X-ray system for taking short exposure X-ray photographs comprising an X-ray tube having an anode and a cathode subjected to high potential electrical energy upon energization of said tube, a source of grounded unidirectional high potential energy having a potential with respect to ground at least no greater than one half the total potential of said source for supplying a positive potential to the anode and a negative potential to the cathode of said X-ray tube, a thermionic discharge device provided with an anode, a cathode, and a grid and interposed between said source and the anode of said X-ray tube, said device having a current voltage characteristic corresponding to that of said X-ray tube and subjected to the same positive potential supplied by said source to the anode of said X-ray tube and to a potential corresponding to that of said source with respect to ground, an auxiliary source of electrical energy connected to the grid of said discharge device and normally operative to impress a negative potential upon said grid to prevent a high positive potential 'being supplied by said high potential source to the anode of said X-ray tube, an auxiliary source of potential adapted to be connected to the grid of said discharge device for impressing a posia grid, and interposed between said source and.

the cathode of said X-ray tube, said device having a current voltage characteristic corresponding to that of said X-ray tube and subjected to the same negative potential supplied by said source to the cathode of said X-ray tube and to a potential corresponding to that of said source with respect to ground, an auxiliary source of electrical energy connected to the grid of said last mentioned discharge device and normally operative to impress a negative potential upon said grid to prevent a high negative potential being supplied by said high potential source to the cathode of said X-ray tube, an auxiliary source of potential adapted to be connected to the grid of said second mentioned discharge device for impressing a positive potential thereupon, and a relay electrically associated with all of said auxiliary sources and operable in response to actuation by an operator to cause both said auxiliary sources supplying a negative po-- tential to the grids of the respective discharge devices to become ineffective and to connect the remaining auxiliary sources to the grids of the respective discharge devices for the purpose of impressing a positive potential thereupon to enable said high potential source to supply a positive and negative potential to said X-ray tube and energize the same.

' WILLIAM A. McKAY. 

